12V batteries have historically always been subject to frequent replacements connected to warranty claims, thus leading to very high costs. There are several different reasons to why batteries are replaced before the warranty period has passed. One of the main reasons for these replacements is due to inaccurate judgements by the battery testing methods used in workshops.
Constructing a battery test that is both quick and can be performed without removing the battery from the vehicle is difficult. Accurate battery testing methods typically takes days and requires large testing equipment, which is both expensive and stationary. A handheld battery tester commonly used to determine the health of a battery connected to the warranty claim utilizes high frequency and low voltage to calculate the impedance of the battery. The impedance can in turn, to some extent, be used to determine the health of the battery. However, due to the fact that the handheld tester cannot discharge or charge the battery, nor does it take temperature or state-of-charge into account, making it less reliable.
A more thorough lab-based evaluation of batteries which had been discarded by a conventional handheld tester showed that a large portion of the batteries were only low on charge and still had more than enough capacity to continue service.
Accordingly, it is desirable to provide an improved method for determining the status of a battery in a vehicle to avoid discarding functioning batteries before the actual end-of-life of the battery.
U.S. Pat. No. 6,424,158 discloses a method and system for performing automatic and rapid diagnostic testing and charging of a battery utilizing a charger combined with a rapidly variable load. The method involves measuring currents at different voltage levels. However, the results from the disclosed battery tester are still not sufficiently accurate.